diff --git a/code/useful_functions.py b/code/useful_functions.py
index 4038291..1ada50a 100644
--- a/code/useful_functions.py
+++ b/code/useful_functions.py
@@ -54,7 +54,7 @@ def binary_spikes(spike_times, duration, dt):
     binary[spike_indices] = 1 # put the indices into binary
     return binary
 
-def calculate_integral(freq, power, point, delta):   
+def calculate_integral(freq, power, point, delta = 2.5):   
     """
     Calculate the integral around a single specified point.
 
@@ -66,8 +66,8 @@ def calculate_integral(freq, power, point, delta):
         An array of power spectral density values.
     point : float
         The harmonic frequency at which to calculate the integral.
-    delta : float
-        Radius of the range for integration around the point.
+    delta : float, optional
+        Radius of the range for integration around the point. The default is 2.5.
 
     Returns
     -------